Auto white balance (AWB) processing is performed immediately after an electronic camera is turned on in a motion-picture-capturing mode, and an image being captured (a through image) is displayed on a liquid crystal monitor. When an image-capturing switch is pressed and an instruction to prepare for image-capturing is entered, white balance is fixed by performing AWB processing, and a motion picture is captured in response to an instruction to start the image-capturing. During the capturing of the motion picture, periodical AWB processing is not performed, an evaluation value for AE is obtained on a regular basis, and when the evaluation value changes by more than a predetermined value, the AWB processing is performed again. Thus, a load of processing is reduced for a control unit (CPU) included in the electronic camera, which can capture a motion picture, and the cost is also reduced. Moreover, a good image can be attained by making a white balance adjustment react instantaneously to a big change in a scene being captured.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for controlling auto white balance of an electronic camera for capturing a motion picture, comprising: performing an auto white balance processing at a beginning of capturing of the motion picture and fixing white balance control values; monitoring an evaluation value for an automatic exposure control while continuing the capturing of the motion picture with the fixed white balance control values; when the evaluation value for the automatic exposure control changes by more than a predetermined value, performing the auto white balance processing again and resetting the fixed white balance control values.
2. An electronic camera, comprising: an imaging device which converts an optical image of a subject into an image signal; an evaluation value calculation device which calculates an evaluation value for an automatic exposure control according to the image signal obtained from the imaging device; a white balance control value calculation device which calculates a white balance control value for each color channel according to the image signal obtained through the imaging device; a white balance adjustment device which performs a white balance adjustment by controlling a signal from each color channel according to the calculated white balance control value for each color channel; and a controlling device which controls to perform an auto white balance processing by operating the evaluation value calculation device, the white balance control value calculation device and the white balance adjustment device at a beginning of capturing of a motion picture and to fix the white balance control value for each color channel according to a processing result, monitors the evaluation value for the automatic exposure control during the capturing of the motion picture with the fixed white balance control values for each color channel, and when the evaluation value changes by more than a predetermined value, performs auto white balance processing again and resets the fixed white balance control value for each color channel according to a result of performing the auto white balance processing again.
3. The electronic camera according to claim 2 , further comprising: an evaluation value storage device which stores the evaluation value obtained at a moment of performing auto white balance processing, wherein the controlling device determines whether auto white balance is to be performed again or not by comparing the evaluation value stored in the evaluation value storage device with the evaluation value obtained while the motion picture is captured, and when auto white balance processing is performed again, rewrites the evaluation value stored in the evaluation value storage device with a new evaluation value.
4. A method for controlling an auto white balance process of an electronic camera, comprising: initially determining reference white balance control values; initially determining a reference exposure value; starting a motion picture capture process after both the reference white balance control values and the reference exposure value are initially determined; and while the motion picture capture process is occurring, repeating the steps of: performing the auto white balance process based on the reference white balance control values; determining a new exposure value; determining if a difference between the new exposure value and the reference exposure value is greater than a predetermined amount; setting the new exposure value as the reference exposure value when it is determined that the difference between the new exposure value and the reference exposure value is greater than the predetermined amount; and determining new auto white balance control values and setting the new auto white balance control values as the reference white balance control values when it is determined that the difference between the new exposure value and the reference exposure value is greater than the predetermined amount.
5. The method for controlling the auto white balance of the electronic camera according to claim 4 , wherein the step of determining the new white balance control values comprises: dividing an image frame into a plurality of areas; calculating an average integrated RGB values for colors RGB for each of the plurality of areas; and determining RGB gain values for the colors RGB such that a ratio R:G:B of the image frame is substantially a predetermined desired R:G:B ratio, wherein the RGB gain values are the new white balance control values.
6. The method for controlling the auto white balance of the electronic camera according to claim 5 , wherein the predetermined desired R:G:B ratio is 1:1:1.
7. The method for controlling the auto white balance of the electronic camera according to claim 5 , wherein the step of determining the RGB gain values for the colors RGB such that the ratio R:G:B of the image frame is substantially the predetermined desired R:G:B ratio comprises: calculating ratios R/G and B/G for each of the plurality of areas based on the average integrated RGB values for the colors RGB for each of the plurality of areas; and calculating the gain for each of the colors RGB based on the calculated ratios R/G and B/G.
8. The method for controlling the auto white balance of the electronic camera according to claim 5 , wherein the step of determining the gain for each of the colors RGB such that the ratio R:G:B of the image frame is substantially the predetermined desired R:G:B ratio comprises: calculating color difference signals R-Y and B-Y for each of the plurality of areas based on the average integrated RGB values for the colors RGB for each of the plurality of areas; and calculating the gain for each of the colors RGB based on the calculated ratios R/G and B/G.
9. The method for controlling the auto white balance of the electronic camera according to claim 4 , wherein the step of performing the auto white balance process based on the reference white balance control values comprises: setting a gain value for each color RGB based on the reference white balance control values for an input image frame; and multiplying each color RGB of each pixel of the input image frame by the respective gain value to output an output image frame.
10. The method for controlling the auto white balance of the electronic camera according to claim 4 , wherein the step of determining a new exposure value comprises: detecting a brightness of a subject; and calculating the new exposure value appropriate to capture the subject in an image frame based on the brightness of the subject.
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May 27, 2003
February 12, 2008
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